1. Field of the Invention
The present invention relates to a circularly-polarized-wave flat antenna having a large number of circularly-polarized-wave antenna elements protruding on the outer surface of a metal plate of a waveguide power distributor.
2. Description of the Related Art
In recent years, a variety of communication systems and broadcasting systems using circularly-polarized microwaves have been proposed. Accordingly, a variety of circularly-polarized-wave antennas for transmitting and receiving circularly polarized microwaves have been studied and developed. One of the circularly-polarized-wave antennas, a circularly-polarized-wave flat antenna using curl antenna elements has been proposed.
More specifically, the circularly-polarized-wave flat antenna has a hollow disc-shaped waveguide constructed of two disc-shaped metal plates equally spaced by a predetermined distance. The waveguide and a power feeding member disposed at the middle of a first metal plate construct a waveguide power distributor. On the outer surface of a second metal plate, a curl antenna array consisting of a large number of curl antenna elements is disposed. Each curl antenna element comprises a shaft portion and a helical curl portion. One end of the shaft portion extends almost vertically from the second metal plate. The other end of the shaft portion is inserted into the waveguide. The other end of the shaft portion is insulated from the waveguide. The curl portion is curled for 1 to 1.5 turns and connected to the protruded end of the shaft portion. The curl antenna element array is separated into a plurality of rows disposed in a ring shape about the center of the second metal plate.
Microwaves are received by the curl portion and the protruded end of the shaft portion of each curl antenna element. The received microwaves are sent to the power feeding member through the inserted portion of the shaft portion and the waveguide. In the case of transmission, signals received from a transmitter are sent to the curl portion and the protruded portion of the shaft portion through the waveguide and the inserted portion of the shaft portion. Thus, circularly polarized microwaves are radiated from the curl portion and the protruded portion of each curl antenna element.
With respect to the circularly-polarized-wave flat antenna, the phases of circularly polarized waves radiated from all the curl antenna elements should match each other. Thus, the orientation of the curl portion of each curl antenna element, that is, the direction about the shaft portion of the curl antenna element, depends on its position disposed on the metal plate. Therefore, the curl portion of each curl antenna element should be oriented in a predetermined direction.
As a result, it is desired to simplify the operation for mounting a large number of curl antenna elements on the metal plate in different directions according to predetermined positions.